Maria Butina, an apparent pro-gun rights campaigner, took part in a "years-long conspiracy" to secretly work in America on behalf of the Russian government, United States prosecutors have claimed.

Butina's arrest was announced as Trump flew back from Helsinki to Washington, following an inaugural summit with Putin.

Prosecutor Erik Kenerson told the court that "the evidence is overwhelming the defendant was here on behalf of the government of Russia.to carry out a covert influence campaign".

The Justice Department said Ms Butina has been in contact with Russian intelligence operatives, kept contact information for several Russian agents and had a handwritten note in her Washington apartment asking how to respond to an offer of employment with a Russian intelligence agency.

In a new court filing, the Federal Bureau of Investigation alleges that Butina during her time in the United States cohabitated with an unidentified 56-year-old man as part of her cover while conducting her work in the United States.

Butina told the Senate Intelligence Committee that she began a romantic relationship with Erickson, people familiar with her testimony said, and investigators believed she may have meant to go to Erickson's home state of South Dakota before she was arrested. She is scheduled for a detention hearing Wednesday afternoon on whether to release her from jail before trial, and prosecutors filed a motion this morning outlining why she should be held without bond.

Butina's lawyer Robert Driscoll said the charges were overblown, saying she was just a student who "at most" wanted a better relationship between the USA and Russian Federation. That official, who left the U.S. in March, was suspected of being a Russian intelligence officer, according to prosecutors.

"Unrelated to specific presidential campaigns, I've been involved in securing a VERY private line of communication between the Kremlin and key POLITICAL PARTY 1 leaders through, of all conduits, the [GUN RIGHTS ORGANIZATION]", he wrote.

Butina has not been charged with espionage or with being a member of a Russian intelligence service.

Butina is also a gun rights activist in Russian Federation and a former gun store owner. Authorities added that Butina has ties to wealthy businessmen in the Russian oligarchy.

An alleged Russian spy is said to have exchanged sex for a position within a special interest organisation. "Further, in papers seized by the FBI, Butina complained about living with Person 1". That individual appears to fit the profile of Alexander Torshin, a former senator and Russian central banker who was sanctioned by the U.S. Treasury Department earlier this year.

It was apparent Butina was getting ready to leave Washington, the United States said.

The charges against Butina were made public just hours after President Donald Trump appeared to accept assurances from Russian President Vladimir Putin that his country did not try to influence the 2016 election.

The NRA, which has previously been connected to Butina, has not commented on the charges.